Freezer bag on the basis of black body radiator

ABSTRACT

A preferably dark coated freezer storage bag on the basis of a black body radiator and a method of making it. The freezer bag is coated on the outside with a coating having a thermal emissivity higher than 0.56, mostly used black 100% virgin polyethylene with an emissivity of (ε=0.92) or black carbon with an emissivity of (ε=0.88). The invention pertains to a process of minimising the freezing and defrosting time of foodstuff inside and outside the refrigerators by optimising the thermal transfer.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to a black coloured freezer storage bag. Theoutside of the bag is coated with a black pigment or the pigment iscombined with the polymer structure of the foil. During the freezingprocess the dark coloured outside of the bag enables to a higheremission of thermal radiation and reduces the freezing time of thefoodstuff compared with standard sizes of mostly transparent freezerbags. The black freezer bag is functioning on the basis of a black bodyradiator. It maximises the emission of thermal radiation during thefreezing process and minimises the defrosting time due to its highergrade of absorption of thermal radiation when being outside therefrigerator in contact with a higher ambient temperature.

2. Description of the Prior Art

Freezer bags made out of plastic already exists in various versions. Themostly performed standard size of a freezer bag is made of transparentpolyethylene foil. The main function of standard freezer bags is theprevention of the so called freezer burn (see “Packaging Foods WithPlastics”, by Wilmer A. Jenkins and James P. Harrington, published in1991 by Technomic Publishing Co., Inc., at page 305).

The patent applications CA2162681/EP877051 relates to copolymers ofethylene and a C4-C12 monomer having a relatively narrow compositiondistribution and to the production and use of such copolymers. Itrelates to linear low density polyethylene resins (LLDPE) that have muchbetter processability and film properties like clarity, gloss and lowreblock. The application do not relate to any solution to produce apolyethylene foil with a higher grade of thermal emission on the basisof black-body radiators.

The application WO1997029966/EP880457 made by S. C. Johnson/Dowbrandscomprises a freezer multibag that consists of a inner liner bag and anouter support bag to reduce freezer burn. The use of multibags does notrelate to any improvement of thermal emission of radiation and areduction of freezing time.

The application U.S. Pat. No. 5,840,800 relates to improvements inpolymer foil production and leads to an aqueous dispersion ofcrosslinked pre-formed silicon modified organic polymer which upondrying, yields to an elastomer, but it does not give a solution to anincreasing thermal emission of radiation.

DE69232195 relates to a freezing mould bag. It leads to ice cubes with adefined shape and give no answer to the essential problem solved by thepresent invention.

The patent application DE2658150 relates to process of splitting thefruits from its fruit juice during the freezing process and give nosupport for increasing the emission or absorption of thermal radiation.

All standard sizes of freezing storage bags don't give any solutions tothe problem of heat exchange and thermal transfer during the freezingand defrosting process of foodstuff that is packaged in freezing bagsmade of polyethylene.

The applications WO0176976 and WO2005000690 relate to a multilayer heatsealable packaging material for foodstuff that reduces light andUV-transition by using a carbon pigment combined with titanium oxide inone inner layer (not the outside layer) to produce a grey colour of thefoil. The outside surface of such a multilayer composition is glossy andhas no black pigment and the grey colour of the inner layer leads to areduction of thermal emission of radiation.

SUMMARY OF THE INVENTION

The present invention solves the problem described above, by providing ablack coloured freezer storage bag that increases the grade of emissionand absorption of thermal radiation according to the ambienttemperature. It optimises the heat exchange in order to reduce freezingand defrosting time.

DETAILED DESCRIPTION OF THE INVENTION

The problem of the invention is solved by the use of black colouredfreezer storage bags according to the claims 1 to 8.

A possible composition of a multilayer freezer bag comprises:

-   -   a substrate with a thickness from 5 mu m up to 300 mu meter,        which is selected from the group consisting of:    -   a thermoplastic material like 100% virgin polyethylene according        to the US government specification LP378 or conformant to the        FDA regulation 177.1520,    -   an aluminium foil.    -   an outer surface coated with a pigment that has a emissivity        ε>0.56. That might be a dark coloured pigment, especially a        carbon black modification (ε>0.8), like FW200 or inorganic        iron(II,III) oxides (ε=0.56) to increase thermal transfer. But        also white coloured pigments might be for some applications        useful, especially Titanium oxide with Potassium Silicate        (ε=0.92) or Zinc Oxide with Sodium Silicate (ε=0.92).

The emissivity is the ratio of the power W [Watt/m²] or radiation asurface emits into a surrounding hemisphere and the total radiant powera perfect black body radiator emits, given by W₈ [Watt/m²]=σT⁴ whereσ=Stefan-Boltzmann constant. (see: Radiometric Properties of IsothermalDiffuse Wall Cavity Sources, Applied Optics, Vol. 13, page 2142,September 1974).

The given average emissivity values have been taken from the listpublished by Electro Optical Industries, Inc., 859 Ward Drive, SantaBarbara Calif. 93111, www.electro-optical.com.

It is also useful for a higher thermal emission to produce a non bright,mat surface and not glossy like one of the already existing conductivebags.

Useful binders are all polymeric binders used in foodstuff applicationsthat do not hinder thermal transfer and are applicable in temperatureranges that occur in standard refrigerators, like for examplepolysiloxane or polyorganosiloxanes (silicones), especially all sorts ofpolyester and epoxide modified silicone resins. Among these are thepolyester-modified methylphenyl polysiloxanes and hydroxyl functionalsilicone resins published in U.S. Pat. No. 6,696,511 and DE10035641 incombination with aluminium as a substrate. In addition to this a mixtureof hydrolyzable trialkoxysilane and hydrolyzable dialkoxysilane, water,acidifying agent from about 2.8 to 6, published in the 20 years oldapplication U.S. Pat. No. 4,439,239 (page 2, line 5-7; page 4, line25-57; page 9, line 1-32).

Among the binders selected from the group of Polysiloxanes are the socalled inorganic-organic siloxane-based hybrid polymers that encapsulatethe pigment in three-dimensional networks in a Sol-Gel transformation.They are more and more used in foodstuff applications and some examplesare given in the applications WO00/59555 (page 3, line 26 page 8 line1-19, page 9 line 29), EP1201721 (column 1, line 49-61; column 5, line4; column 7, line 14 and examples 1-3) and EP1484372.

Another example of a useful binders consisting of organic-inorganicpolymeric chains that are linked to Ormosil monomers(Fraunhofer-Institut für Silicatforschung ISC Neunerplatz 2;97082Würzburg Germany; www.isc.fhg.de).

For example Tetraethylorthosilicate that is linked to di- tri-ortetrafunctional silicon alkoxides three-dimensional networks by Sol-Geltransformation. More flexible for the use in combination withpolyethylene as a substrate are the Ormocer hybrids published by theFraunhofer Gesellschaft in Munich, Germany.

In addition to this all sorts of acrylate resins, like polyacrylates oracrylate elastomers can be used according to the non-toxic premiss ofthe application.

Another example of a polymer-based composition and useful coating of theoutside of the freezer bag is described in the application WO0177215. Incontradiction to the composition in WO0177215 for the present inventionit is necessary to use only carbon black as a pigment and no titaniumoxide in order to bring the freezer bag into line with a black-bodyradiator.

Another possible composition of a black freezer bag comprises a bag madeout of a thermoplastic 100% virgin polyethylene, especially high densitypolyethylene according to the US government specification LP378 and theFDA regulation 177.1520 that is entirely black coloured, for examplewith carbon black. The average emissivity of black polyethylene isε=0.92 and is high enough for a good energy emission. If a multibag isused as a freezer bag to prevent freezer burn like in applicationWO97/29966 of S. C. Johnson, at least the outside bag must be made outof black polyethylene.

To realize a better thermal transfer from the inside of the bag to thesurface it is useful to take aluminum foil as a substrate. The metalfoil has a much better thermal conductivity compared with polyethyleneas material. The inside of the aluminium foil can be coated with anon-stick surface in order to hinder the sticking of the foodstuff andit also prevents any chemical reaction of the foodstuff and thealuminium.

Especially the freezer bag can be modified as a aluminium container thatcan be closed in an airtight manner. When polyethylene is selected as asubstrate, there can be a small window of transparent polyethylene lefton one side of the bag in order to make the frozen foodstuff clearlyvisible for the user.

The foregoing examples have been presented for the purpose ofillustration and description only and are not to be construed aslimiting the scope of the invention any way.

The scope of invention is to be determined from the claims appendedthereto.

1. Freezer bag on the basis of a black body radiator comprising an outersurface, being coloured with a coating having an thermal emissivityε>0.56, for example carbon black (ε>0.88), black polyethylene (ε>0.9) orwhite Zinc Oxide with Sodium Silicate (ε>0.90) or Iron(II,III) oxide(ε>0.56) or the outer surface is made in its entirety out of 100% virginblack polyethylene.
 2. Freezer bag composition of claim 1, wherein thepolymeric binder for the outer coating is selected from the group of amixture of hydrolyzable trialkoxysilane and hydrolyzable dialkoxysilane,Polysiloxanes or Polyorganosiloxanes, Ormocers or Ormosils andPolyacrylates.
 3. Freezer bag composition of claim 1, wherein thepigment used for the outer coating is encapsulated in thethree-dimensional networks of the polymeric binder by a Sol-Geltransformation.
 4. Freezer bag of composition claim 1, wherein aluminiumfoil with a thickness from 5 mu meter up to 300 mu meter is selected asa substrate.
 5. Freezer bag composition of claim 1, wherein the bag ismodified as a aluminium container that can be closed in an airtightmanner.
 6. Freezer bag of composition claim 1, wherein one side of thebag has a window made of transparent polyethylene to recognize thefoodstuff inside.
 7. A process of accelerated freezing and defrostingfoodstuff, wherein the foodstuff is packaged with a freezer bag on thebasis of a black body radiator.